Pressure vessels made with polyolefin housings are known. See: "LIQUI-CEL.RTM. Extra-Flow 4".times.28"" Membrane Contactor For Process Scale" 1994 Product Bulletin. The housings of these vessels, however, must be machined to create the flanges to which the end caps are secured. Machining of the housings is expensive. A less expensive method for the production of the housings is necessary.
The overmolding process is known. See: U.S. Pat. No. 5,409,655; French Patent No. 2,550,848; and Rohner, M. L. "Injection Weldable Nylons" Society of Plastics Engineers, Inc. Rochester, N.Y., Sep. 15-16, 1993. Typically, in an overmolding process, an elastomer is overmolded onto a substrate (the substrate may be made of metal or rigid plastic). In U.S. Pat. No. 5,409,655, KRAYTON.RTM., a thermoplastic elastomer sold by Shell Oil Company of Houston, Tex., is overmolded onto NORYL.RTM., a modified nylon material sold by General Electric Company of Fairfield, Conn. In French Patent No. 2,550,848, a thermoplastic elastomer (an elastomer based on polypropylene and an ethylene-propylene copolymer) is overmolded onto a polypropylene. In the Rohner article, injection welding grade nylons are overmolded onto nylons.
It is believed by some in the plastic's industry that overmolding of a polyolefin (i.e., the overmolded material) onto a polyolefin (i.e., the substrate or also referred to as an insert) is not possible because a melt interface between the two parts can not be formed without overheating and thereby distorting (e.g., warping or caving in) the substrate. Accordingly, there is a need for a process by which a polyolefin can be overmolded onto a polyolefin substrate.